joe@vwvortex

especially the info on the Haldex system. I've logged over 40k in my TT and 40k on my old Avant. Haldex does not work on slip alone - it also is torque sensing and it's abilities to send torque are much quicker than the mechanical based torsen system. Torque output from the engine is one of the factors which the ECU of the haldex uses when redirecting power front to rear. As for the amount of power of 25% to each wheel on the torsen vs. haldex - both distribute torque side to side using the same EDL sensor open differential system. My sole point is that an electrical system can distribute power quicker than a mechanical system and the amount of power distributed is controlled by electronics not the mechanical limitations of the system. In order to change torsen to move more than 66% of the power - you would need to modify the torsen unit. In the other systems - modifications to programming are all that is needed.

I understand what you mean by the power distribution happening more abruptly with the haldex - it's something that I like about the system. How could torsen be "pro-active"?

Audi Junkie

Only *UP TO* 50% torque to front axle. BRING IT ON!!! All-mechanical quattro will kill it.

Silver Stealth

You are correct about two things:

1. Side to side torque distribution is handled by the same EDL in both systems.

2. Audi's torsen system is limited to 66% at one axle.

Your point about the speed of electronics is true. If Torsen were a part-time system and only engaged when needed, your argument about speed and efficiency would be true. That's not the case, however.

The pro-active part of the torsen system is that you ALWAYS have 50% power at each axle, unlike the TT where it is essentially front-wheel drive until there is slippage (OK, technically it is a 97%:3% bias to the front).
While the Haldex system can quickly react and send power to the rear, it is still REACTING to the situation, no matter how fast it is doing so.
In contrast, when you have equal torque driving both axles, the need for such torque shifting is inherently reduced. You've got the power already there in the first place. That's what I mean by Torsen being pro-active.

RKA

Is 50/50 the ideal torque distribution?

joe@vwvortex

and that is correct. However - to transfer torque - Torsen is a reactive system as it reacts just like other systems. That was my point.

joe@vwvortex

IMO - it's really not necessary for all conditions, say cruising at 80 mph down the freeway on dry pavement since all it is doing is wasting gas through additional drive train losses. In terms of handling dynamics and safety - it does have it's advantages. In terms of pure driving dynamics - it may not be.

RKA

When accelerating, where do you want the torque to go?
Can and electrical based system use sensors to determine what the driver is doing, and what kind of traction is available, hence adjusting torque bias accordingly?
Will chassis weight distribution change using what is inherently a rear wheel drive layout? Can the engine be pushed *behind* the front axle, rather than in front of it...yielding handling improvements and better chassis dynamics?

joe@vwvortex

when accelerating you want the power to go to the wheels which have the best opportunity for moving you forward. However, it will be dependent on the situation at hand. Those systems which can react to the situation the quickest with the least amount of driver input would IMO be the best systems. Both electrical and mechanical systems have their advantages and disadvantages in this respect.

As for the issue of weight distribution, an AWD car will always be heavier than a FWD or RWD car and present issues with weight distribution solely because it has two differentials. In Audi's case - they have taken a FWD chassis and adapted AWD to it. Their engine and transmission layouts have always been front weight biased due to their layout. They have recently developed transmissions which shift more of the weight behind the front axle to improve distribution but they will always be front biased. As for cars like the G35 which are RWD with the engine behind the front axle to begin with, I would ASSUME that they will incur some front weight penalty since they have to add a differential to power the front wheels. ON previous versions of the Skyline - it was a center differential with a multiplate wet clutch which in turn drove the front wheels. I'm curious to see what the official specs of the new G35 are in terms of weight distribution and overall weight.

When it comes right down to it - IMO the electronically controlled systems which use wetmultiplate clutches like the one pioneered in the Porsche 959, the Skyline and the Haldex system allow for greater driving dynamics.

RKA

considerations at play, which will make the G35 AWD system a success. The 50/50 torque split in the Quattro system can be improved upon.

joe@vwvortex

I like the torsen system alot - especially for bad driving conditions and snow etc. because it's a very safe system in those respects. I'd agree that if the Atessa system in the new G35 is ANYTHING near as good as the system in the previous generation Skylines (G35 IS a Skyline in Japan), then it should be pretty damn nice. Remember I prefer the Haldex system to the Torsen - its just more fun to drive IMO.